1 00:00:00,620 --> 00:00:06,620 Good morning everyone! Today I'm going to review with you this unit about heat and light. 2 00:00:06,620 --> 00:00:12,619 Heat is the transmission of thermal energy. 3 00:00:12,619 --> 00:00:18,620 As you saw in your experiment, heat makes particles move faster. 4 00:00:18,620 --> 00:00:22,620 This movement makes different things happen. 5 00:00:22,620 --> 00:00:30,800 For example, heat is transmitted in three different ways, if you remember, it always 6 00:00:30,800 --> 00:00:37,159 transmits from a hot object to a colder object. 7 00:00:37,159 --> 00:00:43,460 And the three ways in which the heat transmits are conduction, do you remember, like when 8 00:00:43,460 --> 00:00:49,859 you're cooking something and it's in touch with something hot, it becomes hot. 9 00:00:49,859 --> 00:00:53,579 So for conduction, the two objects have to be in contact. 10 00:00:54,380 --> 00:00:58,679 Then we have convection, which happens in liquids and gases. 11 00:00:58,679 --> 00:01:05,680 This drawing is to remind you about boiling water. 12 00:01:06,519 --> 00:01:19,840 When you see boiling water, it's because the water next to the source of heat is hotter, it moves faster, it goes up, and then it cools down and goes down. 13 00:01:19,859 --> 00:01:38,739 So making this circular movement. Then we have radiation. Radiation doesn't need anything to be transmitted. It can be transmitted in space, where we don't have any matter. Radiation is the heat we receive from the sun travels through radiation. 14 00:01:38,739 --> 00:02:07,019 Remember that some materials are the conductors, materials that transmit heat easily, like for example metal, and then we have the insulators, materials that don't transmit heat easily, for example wood or some plastics, what in Spanish we call the aislantes, insulators, the ones that we use for the oven, for touching things that are hot. 15 00:02:07,019 --> 00:02:18,419 Okay, then, as particles move faster, this causes changes in materials, okay, the effects of heat, which are of three different ways, okay? 16 00:02:18,620 --> 00:02:28,939 We have the changes of state, these are physical changes, you know them from other courses, they are physical because they can be reversed, okay? 17 00:02:28,939 --> 00:02:36,659 If we have ice and we heat it, it melts and we have liquid, we heat it, it evaporates and we have gas. 18 00:02:37,020 --> 00:02:44,439 But if we cool down the gas it becomes liquid again, if we cool down the liquid it becomes 19 00:02:44,439 --> 00:02:48,520 solid again, so it's reversible. 20 00:02:48,520 --> 00:02:54,139 Then we have the expansion, some materials can be expanded with heat, like for example 21 00:02:54,139 --> 00:02:58,460 the example of the trail, of the railway. 22 00:02:58,460 --> 00:03:04,039 And then we have the chemical changes, chemical changes can't be reversed, we have the examples 23 00:03:04,039 --> 00:03:10,580 of when you're making a cake. You do the daff, then you heat it in the oven, and you have 24 00:03:10,580 --> 00:03:16,560 your cake. But it cannot be reversed. You cannot put the cake in the freezer, for example, 25 00:03:16,560 --> 00:03:21,479 and then have the daff again, with the flour and the sugar and the eggs. 26 00:03:21,479 --> 00:03:28,879 Okay, the same with, for example, paper. If you burn paper, it becomes ashes and smoke. 27 00:03:28,879 --> 00:03:33,620 If you put the ashes and smoke back in the fridge or somewhere you cool it down, it doesn't 28 00:03:33,620 --> 00:03:38,780 become paper again. So these changes are chemical, they can't be reversed. 29 00:03:38,780 --> 00:03:43,240 These are the important things about heat. Let's review the things about 30 00:03:43,240 --> 00:03:52,039 light. Light is a form of radiant energy. Light travels very 31 00:03:52,039 --> 00:03:57,020 fast, is the element that we know that travels the fastest in the universe, and 32 00:03:57,020 --> 00:04:02,240 it travels in the form of electromagnetic waves. So it can travel 33 00:04:02,240 --> 00:04:08,840 also in the space. It doesn't need any material to be transmitted. It travels in 34 00:04:08,840 --> 00:04:17,720 straight lines and thus it hits objects. And thanks to the light hitting 35 00:04:17,720 --> 00:04:22,860 objects we can see the objects. As we see the objects there are three 36 00:04:22,860 --> 00:04:28,639 different types of objects according to how light hits them. We have the opaque 37 00:04:28,639 --> 00:04:35,420 objects or materials these are the ones that block the light and project a 38 00:04:35,420 --> 00:04:41,959 shadow okay light don't passes through them don't pass through them then we 39 00:04:41,959 --> 00:04:48,500 have the translucent materials which let a little light pass through and then we 40 00:04:48,500 --> 00:04:54,560 have the transparent materials which let all the light pass through okay this is 41 00:04:54,560 --> 00:04:58,560 Then we have the basic laws of light, which are reflection. 42 00:04:58,560 --> 00:05:06,560 Light, when it hits some special, very smooth surfaces, can be reflected, can change direction. 43 00:05:06,560 --> 00:05:12,560 Light can also change a little the direction when it travels through a different element, 44 00:05:12,560 --> 00:05:15,560 for example, from the air to a liquid. 45 00:05:15,560 --> 00:05:21,560 And then we have the white light, which contains all the colours we can see, the spectrum. 46 00:05:21,560 --> 00:05:28,060 When the white light passes through a person, we can see the different rainbow, the colors 47 00:05:28,060 --> 00:05:32,019 of the rainbow spectrum, all the colors that we can see. 48 00:05:32,019 --> 00:05:34,079 There are more colors, but we cannot see them. 49 00:05:34,079 --> 00:05:40,459 There are the ultraviolet and the infrared, there are different ways that we cannot see. 50 00:05:40,459 --> 00:05:44,360 So these are the important things about heat and light. 51 00:05:44,360 --> 00:05:45,040 See you later!